Coronary heart disease (CHD), affecting about 6% of general adult population, is a common cardiac disorder associated with coronary artery stenosis—the narrowing of coronary artery typically caused by a portion of the lumen of the coronary artery being blocked by plaque. For example, FIG. 1 shows an artery at the heart's anterior surface which has a narrowing lumen as a result of a build-up of cholesterol plaque at its inner wall. This causes a reduced blood supply to the heart.
In U.S., among populations aged more than 65 years old, the prevalence of CHD increases to 19.8% in 2010. CHD causes 1.2 million heart attacks annually and nearly 19% of deaths in US. In Singapore, cardiovascular disease (CVD) accounted for 30.4% of all deaths in 2011, among these, 19% are due to CHD. Therefore, timely and accurate evaluation of suspected CHD patients is among the keys to improving patient care, reducing costs and improving efficiency in care delivery.
There are existing methods in assessing coronary artery stenosis. In particular, invasive coronary angiography (ICA) is the gold standard method for the delineation of anatomical coronary artery stenosis. FIG. 2 shows equipment used in ICA and a resultant image. Fractional flow reserve (FFR) measurement with pressure wire is the gold standard for the assessment of the physiological importance of an anatomical stenosis. The FFR measurement may be performed concurrently with ICA. Non-invasive computed tomography angiography (CTA) is a popular diagnostic alternative to ICA. In CTA, a sequence of two-dimensional (2D) images may be obtained by scans and a three-dimensional image volume (i.e. a stack of the 2D images) may be constructed. FIG. 3 shows equipment used in CTA and a resultant image. A brief comparison of advantages and disadvantages of these modalities is shown in Table 1 below.
TABLE 1A comparison of ICA/FFR and CTAModalityICA and FFR measureCTAAdvantagesAccurate, current goldOutpatient examinationstandardNon-invasive, easy to acceptQuantitativeVery high sensitivitySeamless connectionLow cost (~S$1,100 per exam)with therapyDisadvantagesInpatient procedureNeed expert interpretationInvasive, risk ofLess accurate, prone to over-complicationratingHigh cost (~S$6,000per procedure)Labor intensive (i.e.involves cardiologists,radiologists, technicians,and nurses)
FIG. 4 is a flow chart illustrating the current standard clinical protocol for CHD patient care. CTA scan is performed on suspected CHD patients first. If severe artery stenosis is detected, a subsequent ICA/FFR will be performed. If the severity of the lesion is confirmed by ICA/FFR, stenting or other therapeutic intervention may be performed during the procedure.
CTA enables visualization of the coronary vessels in two-dimensional (2D) or three-dimensional (3D) formats but currently available CTA-based imaging techniques are limited in their abilities in assessing physiological stenosis. Currently, CTA data are interpreted by a radiologist or cardiologist and the severity of a coronary artery stenosis lesion is rated based on a parameter called percent Diameter Stenosis (DS). In particular, a range of DS is used, namely, <25%, 25-40%, 40-70%, >70%.
As illustrated by FIG. 5, DS is obtained by 2D quantitative coronary angiography (QCA), in which images are projected unto multiple planes and the arterial lumen diameter is assessed accordingly. Several clinical studies have reported that CTA has a very high sensitivity and negative prediction value in assessing coronary artery stenosis, but with a lower specificity and positive predication rate [1-4].
While CTA may be a reliable tool to rule out significant coronary artery stenosis, the CTA-based assessment of stenosis lacks precision. It requires an expert's interpretation of the image which may be subjective, and is often operator-dependent. This results in a significant number of false positive diagnoses or over-estimation, and often lead to unnecessary further tests (e.g. costly ICA and FFR) and/or treatments (e.g. stenting) being performed.
Therefore, it is desirable to provide an improved method and apparatus which provide a more accurate assessment of coronary artery stenosis.